1. Field of the Invention
The present invention relates generally to protective devices for beverage dispensing systems, particularly those systems for drawing liquids, such as beer, from containers, such as beer kegs or barrels, using a gas to drive the liquid from the container. More particularly the present invention relates to a novel protective device including redundant safety relief valves for precluding ingress of gas above a predetermined pressure into the keg and regulating the gas pressure within the keg to maintain a predetermined keg pressure thereby to maintain the quality of the beer issued from the keg.
2. Discussion of the Prior Art
Failure of a fluid pressurization system in a keg or like container tapping system can result in large surges of highly pressurized gas flowing through the tapping system into the keg. Keg overpressurization beyond safe limits can and has in the past resulted in the explosion of the keg causing serious injuries and even fatalities. Overpressurization also causes the kegs, due to their peculiar shape, to elongate thus making complete withdrawal of the beer from the keg virtually impossible utilizing existing tapping equipment.
Because of the variety of keg or container sizes, designs, materials of construction, histories of use and abuse, states of structural fatigue, a precise maximum safe internal pressure has been difficult to determine. Also, the degree of hazard associated with a structural failure of the keg or container varies with the degree to which the liquid has already been drawn from the keg, i.e., the quantity of remaining gas volume. An internal pressure of 60 psi gauge is generally considered the maximum safe upper limit. However, when high gas pressures obtain in the keg, albeit within the safe limit of 60 psi gauge, overcarbonization of the beer may occur resulting in a change in the taste of the beer. Surges of gas pressure into the keg thus deleteriously affect the quality of the beer withdrawn from the keg.
There are two sources of keg pressurization, (1) internally generated pressure resulting from the evolution of CO2 gas normally dissolved in the beer, and (2) the gas pressure supplied through the tapping system from an external source. The first is not considered as a source of keg overpressurization sufficient to explode the keg as extreme temperatures, unlikely to occur, would have to be obtained before the maximum safe pressure could be realized. The more common danger of keg explosion as well as reduction in the quality of the beer due to excess pressure, is a result of the use of high pressure air or CO2 bottles as the gas pressurization source.
It has been found that excessive pressures in systems utilizing the CO2 bottle are caused by (a) mechanical failure of the pressure regulator to shut off completely when a predetermined pressure is obtained, and (b) full open mechanical failure of the regulator which usually results from structural failure of the pressure diaphragm. Excessive pressure can also be caused by human error in turning the regulator adjustment in the wrong direction or by inverting the CO2 bottle. In regulators, prevalent cause of failure is contamination resulting from beer backed up into the gas feed line during tapping. Thus, in those systems wherein the beer has backed up, the beer contaminates and corrodes the valve often times in a manner precluding full shutoff. Full open failure of the regulator has also occurred. An appreciation of the consequences of such a faiure can be obtained by noting that a conventional and commonly employed CO2 bottle in tapping beer kegs and the like is capable of dumping its full capacity of gas under pressure, for example, in certain instances about 900 psi gauge into a keg in less than 1 second. It has been found in actual tests that a half-barrel keg in poor condition and 90% full would rupture under the foregoing conditions approximately 0.9 seconds after failure of the regulator and that the same keg 10% full would rupture in approximately 8 seconds.
Pressure relief devices have been provided in tapping units in the past purportedly for the purpose of dumping the excess gas, when a failure occurs, before the maximum safe pressure of the keg is exceeded. For example, a pressure relief valve has been provided in the coupler of the tapping assembly described and illustrated in U.S. Pat. No. 3,288,413. However, it has been found, after stringent examination of this type of valve and its operation, that overpressurization of the keg beyond the maximum safe keg pressure is, in fact, not prevented. The relief valve has been found to be ineffective as (1) its orifice is simply not large enough to dump the pressure quickly enough to preclude overpressurization of the keg beyond the maximum safe pressure, (2) the spring which biases the valve structure into a closed position actually decreases the orifice size in response to increasing pressure due to the closing of the coils, and (3) the pressure at which the relief valve opens changes due to setting of the O-ring seal over the course of use of the coupler. As a result, this pressure relief valve has been found to be unsatisfactory.
One of the most successful beer keg safety systems ever devised is that described and claimed in U.S. Pat. No. 3,848,631 issued to the present inventors. However, the invention as described herein constitutes a substantial improvement over the device described in this earlier issued patent.
As will be more fully discussed in the paragraphs which follow, the present invention significantly improves the safety features of the earlier patented device and provides a novel and improved system for beverage dispensing, particularly beer dispensing systems which overcomes or minimizes the previous problems associated with prior beer tapping systems. More particularly the present invention provides a protective device which includes a secondary safety pressure relieving assembly and (a) positively precludes overpressurization of the keg and keg explosion even if the primary seat of the device should leak or fail; (2) precludes diminution of the quality of the beer withdrawn from the keg by maintaining a predetermined normal tapping pressure in the keg; and (3) automatically regulates and maintains the normal keg tapping pressure irrespective of the pressure of the gas supplied to the keg.